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51. What is the mass of 4.2 kg of gold when it is transferred to a planet having twice the gravity of earth?

71. You have a mixture of salt and sand that must be separated by using physical changes only. Describe what you would do to prepare dry samples of the two constituents of the mixture.

  • chemistry -

    51. Wouldn't the mass be 2 x 4.2 kg?
    71. Salt and sand. Salt dissolves in water, sand doesn't. Couldn't you use that physical property to separate them?

  • chemistry -

    Mass and weight are two different things. It is true that the object would weigh twice as much, but the mass would remain the same, as it is independent of gravity.

    Think of mass as a measure of the amount of matter in an object. Weight is a measure of force (F=ma).

    I agree on the other one. Salt (NaCl) is very soluble in water, and sand (SiO2) is mostly insoluble.

  • chemistry -

    Ian is absolutely correct. I missed that the problem asked for mass and not weight.

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